Re: [PATCH v4 5/6] KVM: MMU: combine guest pte read between walk and pte prefetch

Avi Kivity
2010-07-03T12:44:52Z

On 07/03/2010 03:31 PM, Xiao Guangrong wrote:
>
> Avi Kivity wrote:
>
>
>>>
>>>
>> if (!direct) {
>> r = kvm_read_guest_atomic(vcpu->kvm,
>> gw->pte_gpa[level - 2],
>> &curr_pte, sizeof(curr_pte));
>> if (r || curr_pte != gw->ptes[level - 2]) {
>> kvm_mmu_put_page(shadow_page, sptep);
>> kvm_release_pfn_clean(pfn);
>> sptep = NULL;
>> break;
>> }
>> }
>>
>> the code you moved... under what scenario is it not sufficient?
>>
>>
> I not move those code, just use common function instead, that it's
> FNAME(check_level_mapping)(), there are do the same work.
>
> And this check is not sufficient, since it's only checked if the
> mapping is zapped or not exist, for other words only when broken this
> judgment:
> is_shadow_present_pte(*sptep)&& !is_large_pte(*sptep)
>
> but if the middle level is present and it's not the large mapping,
> this check is skipped.
>

Well, in the description, it looked like everything was using small
pages (in kvm, level=1 means PTE level, we need to change this one
day). Please describe again and say exactly when the guest or host uses
large pages.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.